Case-hardening composition and method of preparing the same



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Patented Aug. I925.

IRA H. DERBY AND CARLETON B. EDWARDS, OF INDIANAPOLIS, INDIANA, ASSIGNORS T0 PETER C. REILLY, O33 INDIANAPOLIS, INDIANA.

CASE-HARDENING COMFOSI'IION AND METHOD OI PREPARING THE SAME.

No Drawing.

To all whom it may concern:

Be it known that we, IRA I-I. DERBY and GARLETON B. Enwnnns, citizens of the United States, residing at Indianapolis, in the county of Marion and State of Indiana, have invented certain new and useful Improve ments in Case-I-Iardening Composition and Methods of Preparing the Same, of which the following is a specification.

This invention pertains to an improved case hardening composition and to the method of preparing the. same.

It has for its main object the production of a material which is highly efficient in operation and stable in use, the invention also permitting the use of materials having high efliciency as activating agents and in quantities heretofore unknown.

As will hereinafter appear, the material or composition is free of any deleterious ef fect upon the metal undergoing treatment and moreover may be used over and over for a considerable period of time, Without substantial deterioration.

These are the essential features of the present invention, but many other advantages inhere as will be apparent from the following description.

Many compositions now used for carburizing or case hardening steel in the so-called pack hardening process consist of a carbonaceous base, such as wood charcoal, or coke, or both, in granular form, on the surface of which has been placed an activator, such as barium carbonate, sodium carbonate, calcium carbonate, lime etc, or a miizture of such activators. Sometimes the chemical activator is smeared on with a sticky binder such as molasses; sometimes it is dusted on. Or, the coke or charcoal may contain the activator impregnated throughout its structure. In the case'of impregnated....charcoal, the impregnation may be made before or after the charring and is usually brought about by soaking the material in a water solution or suspension of the chemical. In the case of impregnated coke, this impregnation is produced by making a mixture of acti vator and powdered coal, or activator and pitch and coking these mixtures. Practically all granular or pellet carburizers, now known to be used, maybe included in one of the above classifications.

In any of these instances, one general characterlstlc is ev1dent; the act1vator, or

Serial No. 641,742.

barium ,aazhonate, cal5i'iirli""c bo'nate and other similar mater1a'ls? "These chemicals may adhere to the steel, causing spots, which are highly undesirable, both because of probable softness of the steel under such spots and because of expense in removing the adhering material. Especially does this adherence of chemicals to the steel occur when sufficient amounts of activators are added t make the carburizing composition rapid in action, a condition which is desired,

Another marked weakness in most carburizing compositions on the market today is the great shrinkage in volume and weight during use, especially during the first use. Shrinkages of twenty-five per cent to forty per cent in volume frequently occur in one run in sealed carburizing boxes, with the ordinary carburizers. Where this shrinkage has been overcome somewhat, it has been at the expense of lightness in weight of the carburizer, which is a decidedly im portant item due to the fact that carburizing compositions are used by volume, not by weight, and the purchase is made by weight.

Still another point in which all of the present carburizers of which we are aware, are weak, is in their decreasing activity during continued use. They fail to yield the same amount of carbon to the steel in successive carburizing heats. In the second and subsequent runs of such carburizers, the oarburizing activity is considerably lower and in three or four heats at most, the carburizer will often be nearly worthless. Especially is this true if no new unused material is added. As hereinafter set forth, we have disclosed a method of manufacturing carburizing material, which is free from the above objectionable. features and also a method by which all of the above objectionable features of any of the present carburizing compositions may be largely eliminated.

Broadly stated, the process forming the basis of the present case resides in covering particles of carburizing material after its preparation, with a porous shell or coating preferably though not necessarily of inactive carbon which entirely covers or coats the carburizing material. The unique feature of this process lies in coating the carburizing material with a non-carburizing material, preferably carbon, such as carbonized pitch, which serves as an insulator to prevent contact bet-ween the materials within the shell and the substance undergoing treat ment. e preferably obtain our product by covering the particles containing activator with a heavy coal tar pitch and carbonizing this pitch. While. this method of coating is the preferred one, it is conceivable in so far as the broad aspect of the invention is concerned, that the shell or coating may be otherwise produced; thus for instance, successive coats of coal tar or oils may be applied, it being understood that such coatings will be carbonized after each application. Other pitches, such as petroleum pitch, wood tar pitch and vegetable oil pitch could be utilized in a single coating. So too, admixtures of pitch and lamp black or pitch and ground carbon of any kind such as ground coke or charcoal may be utilized as the coat ing and shell forming material. In certain cases where there is very little chemical on the surface of the particle or where for other reasons, a thick shell of carbon is not needed, the covering material can be a heavy tar or a light pitch or similar hydrocarbons which of course is afterwards carbonized. A pitch which will yield sixty per cent to eighty per cent of its weight in carbon residue when carbonized, gives the best results and may be put on in a single application. Though the various heavy pitches from petroleum, wood tar, vegetable oils, etc. may also be used, we prefer to make use of coal tar pitch, because it gives a residue consisting of less ash and sulphur and more nearly pure carbon than the others.

In carrying out this procedure, the carburizing particle is coated with fifteen per cent to one hundred and fifty per cent of its weight of pitch such as described, and then heated to a temperature sufficient to drive off the volatile from the pitch and leave a carbon coating or shell entirely surrounding the original carburizing particle. Such acoating successfully prevents any chemical present on or in the original particle from coming in contact with the steel. This same shell of carbon, being sufficiently heavy, persists and continues to function during the repeated continued use of the product in the carburizing process. We have had this carbon shell last and serve its purpose for many runs.

By this invention the activator may be spread upon the basic material and the same covered by the carbon coating. This process obviates the necessity of the use of adhesive material for sticking the activator to the basic material, the shell serving to retain the activator within the product.

The original particle which serves as the support for the chemical may be carbonaceous or not. The shell will supply all carbon necessary to the reaction of carburization and for this reason the supporting particle may be of any solid material which has no injurious effect upon the steel or modifying action of the activator, for instance among carbonaceous materials we may use has coke, petroleum coke, corn cob charcoal, wood. tar coke, and wood charcoal. As an example of a non-carbonaceous supporting particle, we may use dolomitic lime.

We have found that it is very advantageous to shell-coat with carbon the ordinary case hardening compositions on the markets, such as one made from granular wood charcoal and activators such as sodium or barium carbonates, or both; or one made from granular corn cob charcoal and activators; or coke smeared products; or pellets of compound coke; etc. The various advantages here and in our preferred product will be discussed below.

Our method of manufacture of carburizinn; composition which embodies the principle of the shell-coat of carbon is carried out as follows:

We start with sized particles (any or all sizes preferably between two and twenty mesh. standard screens) of any kind of carrier such as charcoal or coke, especially, however, making use of the coal tar coke such as is produced by the process disclosed in U. S. Letters Patent to Reilly No. 1,230,- 82 dated June 19, 1917. This material is substantially pure carbon produced from the distillation of coal tar or coal tar pitch. The material is placed in a concrete or other suitable mixer and thoroughly wet with water, or a soap solution, and a correct amount of chemical for any desired activity is added in powdered form and thus distributed over the surface of the particles. More water is now added to make the particles a little wet, but with no excess water, and the covering material in finely powdered form is added and distributed over the particles. It is not essential, however, that this sequence of steps be followed. The charge then enters a rotary kiln, where it is first dried, the pitch melted and allowed to coat the particles, the volatile distilled and the carbonaceous shell carbonized. YVhen the material leaves the retort at a temperature of 500 C. to 900 C. the operation is complete.

The following variations of the process may be applied: The chemicals are loosely attached to the supporting particle by the evaporation of the water, or soapy water. (leaving the particle coated with caked. chemicals which will break off with hair dling) and melted pitch or other covered is sprayed on to the particle and then carbonized. A porous carbon shell is thus formed. Or we may place the activator on the original particle with water and stick the powdered pitch onto this base with an suitable adhesive material, then heat to melt and carbonize the pitch. It is old to stick the activator onto a carbon particle with an adhesive material, but we believe it is new to stick a pitch coating on with an adhesive material. Or we may stick the chemical activator onto the base with an adhesive material. then add the pitch in any desired way. lVhile the variations just mentioned are feasible and may be carried out in actual practice, we prefer, however, to produce the product by the method as originally set forth.

lVe may also coat both coke and charcoal (sized) in the same operation. To the mixed materials we add water, chemical, water again. and pitch, and then calcine. This coats both materials in one operation, which may be advantageous in certain cases.

Various combinations will suggest themselves of shellcoated products and uncoated materials, in all of which, of course. is included one shell coated product. From a cost or efficiency standpoint it may be advantageous to make up a carburizer containing coke and charcoal. For example, we may place all of the activator upon but one of them and coat only the one holding the activator. Or, we may place activators upon each, coating them separately.

We may also use copper as the non-carbonizing coating material. e have successfully deposited a porous copper shell about the particles of a carburizing composition. lar purpose to the carbon shell. Though in some instances the copper shell may not be as desirable as a shell which is substantially all carbon it may nevertheless be employed. In some cases it may have certain advantages over the carbon shell. It is conceivable, also, that shells of still other compositions may be employed.

From the foregoing it will be seen that many advantages flow from the shell coated materials and they may be briefly stated as follows:

1. Their use removes the danger of adhesions of chemicals to steel and fusions with luting clay.

2. Their use greatly reduces both volume and weight losses of the material during carburizing. This is a very marked advantage that we believe has been accomplished in no other satisfactory way. A

This copper shell serves a simicharcoal carburizing material known to have forty per cent shrinkage when used in the ordinary way was coated and found when so coated, to have practically zero volume shrinkage during identical tests.

3. Little or no chemical activator loss. Most materials ash and dust ofi' considerable amount of the activator each time they are used. The present product very largely eliminates this feature. The shell lasts through many runs, keeping the activator beneath the coating and thus preventing dusting of? of the activator.

4i. Produces a material of long life with little or no loss of activity during continued use. The activator being held intact within the product continues to function at its original activity for a considerable period and except for mechanical losses no new material is necessary.

5. The amount of activator can be greatly increased over that of any other known method. Thus stronger, more active carburizers, can be made by this method. For example, coke containing five per cent sodium carbonate, and charcoal containing ten per cent sodium carbonate have each been found to fuse at 1800 F., while we have used twenty-five to thirty per cent sodium carbonate at 1850 F. without fusion. This also applies to mixtures of sodium carbonate and barium carbonate, which ordinarily fuse at lower temperatures. Many formulas can be utilized that cannot be employed in making carburizers in any other way.

6. A porous shell is produced which allows the gases developed on the inside of the particle to diffuse out but retains the chemicals. This shell does not greatly increase the density of the carburizer. In fact, the shell coated charcoal has practically the same density as the original charcoal and activator. Thus we have the advantage of a light product.

7. In the process of manufacture there are no fines or dust produced by crushing and screening the finished carburized materi a1. We start with granular material and it all becomes a part of the finished granular particle.

8. The protection afforded by the shell permits higher temperatures to be employed in the carburizing operation, and also the use of a larger quantity of sodium carbonate than is now possible by any other process, which features result in shortening the time required for carburization.

9. It is evident that we get efficiency in the production of carbon monoxide, the actual carburizing agent. l/Ve have a miniature gas producer in each carbon shellcoated particle. The carbon dioxide (CO evolved by the activator must pass through the porous carbon shell with which it reacts to form carbon monoxide (CO).

The term shell as employed in this specification and in the appended claims is to be understood as covering and including any coating or covering which encloses the active carburizing material or substance.

hat we claim is:

1. A shell coated carburizing composition.

2. A carburizing composition having a carbon shell.

3. A carburizing composition having a non-carburizing coating.

4-. A carburizing composition having a carbonized hydrocarbon shell.

5. A carburizing composition having a carbon shell free from activators.

6. A carburizing composition having a substantially pure carbon surface.

7. A carburizing composition free from chemical activator at the surface thereof.

8. A carburizing composition having a surface of carbonized pitch.

9. A carburizing composition having a surface of carbonized pitch free from chemical activators.

10. A carburizing composition having a carbonaceous base carrying activators, covered with a protecting shell.

11. A carburizing composition having a carbonaceous base carrying activators, covered with a shell of substantially pure carbon.

12. A carburizing composition having a carbonaceous base carrying activators, covered with a carbonized pitch shell.

13. A carburizing composition having a porous shell.

14. A carburizing composition having a base carrying activators covered with a por ous shell of carbonized pitch.

15. As a new article of manufacture, a carburizing composition comprising a nucleus or body carrying an activator and surrounded by a carbon shell.

16. As a new article of manufacture a granular carburizing composition having a carbon coating.

17. As a new article of manufacture, a granular carburizing composition having an exterior wall or shell formed of porous carbon.

18. That method of producing a carburizing composition which consists in combining an activator with a supporting particle, coating the same with pitch and finally carbonizing the pitch.

19. That method of manufacturing a carburizing composition which consists in producing a substantially pure .carbo n shell around a carburizing material.

20. That method of producing a carburizing material which consists in coating individual particles of the carburizing material with heavy pitch and finally coking the itch.

21. The process of manufacturing a carburizing composition which consists in coating a carbon base with a chemical activator and surrounding the base thus treated with a carbon shell.

22. The process of producing a carburizing material, which consists in coating a carbon base with a chemical activator, surrounding same with pitch. and finally coking the pitch.

In testimony whereof we have signed our names to this specification.

IRA H. DERBY. CARLETON B. EDlVARDS. 

